For many years, curable epoxy resins have been used as components in coating compositions. However, the properties of coatings produced using aqueous epoxy resin dispersions have long been considered inferior to those of coatings in which the resin is used in the form of a solution in an organic solvent. This was mainly attributed to the fact that the emulsifiers used, for example nonylphenol ethoxylates, migrate to the surface of the film where they adversely affect its properties. One way of solving this problem is to use so-called reactive emulsifiers which, where the epoxy resin is crosslinked with a diamine or polyamine or other hardener, react with the hardener and thus become part of the coating. Aqueous dispersions of special reactive emulsifiers are known from the prior art.
U.S. Pat. No. 4,315,044 describes a stable epoxy resin dispersion containing (1) an aqueous medium and (2) between 50 and 70% by weight of a self-emulsifiable epoxy resin which is the addition product of (a) 40 to 90% by weight of diglycidyl ethers of a dihydric phenol, (b) 5 to 35% by weight of a dihydric phenol and (c) 2 to 15% by weight of the diglycidyl ether of a polyoxyalkylene glycol and in which the molecular weight of the epoxy resin is between 500 and 20,000.
U.S. Pat. No. 4,608,406 describes a stable epoxy dispersion containing (1) an aqueous medium and (2) between 50 and 70% by weight of a self-emulsifiable epoxy resin with a molecular weight of 1,000 to 20,000 which is the addition product of (a) 40 to 90% by weight of diglycidyl ethers of a dihydric phenol, (b) 5 to 35% by weight of a dihydric phenol, (c) 2 to 15% by weight of the diglycidyl ether of a polyoxyalkylene glycol and (d) 2 to 15% by weight of an alkyl phenol/formaldehyde/novolak resin.
EP-B-272 595 and DE-A-36 43 751 describe a process for the production and use of stable aqueous epoxy resin dispersions consisting of a) 50 to 80% by weight of an epoxy compound containing at least two epoxy groups per molecule and having an epoxy equivalent weight of 100 to 2,000, b) 35 to 17% by weight of an aromatic polyol and c) 15 to 3% by weight of a condensation product of an aliphatic polyol with a molecular weight (Mw) of 200 to 20,000 and an epoxy compound containing at least two epoxy groups per molecule and having an epoxy equivalent weight of 100 to 2,000, the equivalent ratio of the OH groups to the epoxy groups being from 1:0.85 to 1:3.5 and the epoxy equivalent weight of this condensation product being from 200 to at least 50,000.
WO 95/18165 (Henkel Corp.) describes a self-dispersible curable epoxy resin obtainable by reacting an epoxy resin (a) with a polyoxyalkylene amine (b) with a molecular weight of 3,000 to 15,000. The components mentioned are used in a ratio of (b) to (a) of 0.001:1.0 to 0.060:1.0 equivalent.
WO 96/20970 (Henkel Corp.) describes a self-dispersible curable epoxy resin obtainable by reacting (a) 1.0 equivalent of epoxy resin, (b) 0.01 to 1.0 equivalent of a polyhydric phenol and (c) 0.005 to 0.5 equivalent of an amine/epoxy adduct. The amine/epoxy adduct is a reaction product of 1.0 equivalent of a polyepoxide and 0.3 to 0.9 equivalent of a polyoxyalkylene diamine.
EP-A-747 413 describes a self-emulsifiable epoxy resin (A) obtainable from (A-1) 50 to 95% by weight of one or more epoxy compound(s) containing at least two epoxy groups per molecule and having an epoxy group content of 300 to 11,200 mmoles/kg, (A-2) 5 to 50% by weight of an aromatic polyol, (A-3) 0 to 25% of modifying compounds containing at least two epoxy-reactive groups, (A-4) 5 to 35% of a condensation product—acting as emulsifier—of (A-4-a) an aliphatic polyol with a weight average molecular weight Mw of 200 to 20,000 g/mole and (A-4-b) an epoxy compound containing at least two epoxy groups per molecule and having an epoxy group content of 500 to 10,000 mmoles/kg, the ratio of the number of OH groups to the number of EP groups being from 1:2 to 1:10 and the epoxy group content of the condensation products (A-4) being from 100 to 6,700 mmoles/kg.
The present invention also includes processes for the production of self-dispersing, hardenable epoxy resins.